Recently, a stimulus-responsive hydrogel that gels in response to external stimulus such as heat, pH, light or the like has been expected to be applicable to a broad field as a substrate for tissue regeneration materials and slow-release preparations and as an absorbent for harmful substances, and its studies are being much promoted. In particular, PNIPAM (poly(N-isopropyl acrylamide)) or the like known as a temperature-responsive polymer is known to have LCST (lower critical solution temperature) at or above which the solubility in water of the polymer dramatically lowers, and the presence of a thermal responsive hydrogel to form a hydrogel at or above LCST based on this phenomenon is reported. However, in expecting biological application, the polymer such as PNIPAM has a drawback in that its biodegradability is poor. As opposed to this, a low-molecular hydrogel is expected to reduce the load to living bodies since it is a low-molecular aggregate integrated through the noncovalent bondings such as hydrophobic interaction or hydrogen bonding. Accordingly, the necessity for a temperature-responsive low-molecular hydrogelling agent would increase more and more. However, as an example of its report, there may be found only Non-Patent Reference 1 by Hamachi et al mentioned below.